RMS is the protection component of AIP, that can encrypt and set rights in documents, that persist wherever the document ends up (email, uploaded, copied etc.). Azure Rights Management is included in some Office 365 plans as well. You can compare all these offerings here.
AIP bring labelling and classifying features that extend this to promote easy to use document handling and enforcement, with auto data classification in the top tier option. Other features only in AIP include document tracking and revocation.